Electromagnetism



J. N. GILBERT.

ELECTROMAGNETISM.

APPLICATION FILED APR. 15. I915. 1,323,747. Patented Dec. 2,1919.

4 $HEETSSHEE1 I. ()(JT- m D M-A1 i? A l' n1 ll II L n "3 INVENTOR.

30mm M 25mm J. N. GILBERT.

ELECTROMAGNETISM.

APPLICATION FILED APR. I5, 1915.

Patented Dec. 2,1919.

4 SHEE'TSSHEET 2.

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#:223 372 9 W k 1W 29 1. N. GILBERT.

ELECTROMAGNETISM.

APPLICATION FILED APR. 15, I915.

Patented Dec. 2,1919.

4 SHEETS-SHEET 3.

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J. N. GILBERT. ELECTIROMAGNETISM. APPLICATION FILED APR. 15. 1915.

1,323,747. Patented Dec. 2,1919.

4 SHEETS-SHEET 4.

I VEN TOR.

JOSEPH N. GILBERT, OF IJIINNEAPOLIS, MINNESOTA.

ELECTROMAGNETISM.

Specification of Letters Patent.

Patented Dec. 2, 1919.

Application filed April 15, 1915. Serial No. 21,580.

be produced by alternatin currents. The

application for generating and transmitting electrical energy, filed June 5th, 191%, Serial No. 8 l3,21'l' covers broadly the production of unequal amounts of magnetism corrc-- sponding to the alternations of opposite polarity of an alternating current, which may be carried to the extent that the magnetism may be limited to one sign only. by causi the magnetic enejg applied to the mag netic circuit in which the magnetism is produced, during successive half cycles of different sign of the alternating current, to be unbalanced. According to the present in mmtion this result is attained by supplying a balanced magnetizing energy, such for inare the ordinary alternating current r sine wave form, to a coil or primary on re core to be magnetizing and unbalancing the action ot a secondary coil on said (ore for successive alternations of opposite sign.

Other and ancillary objects of the invention will appear hereinafter.

in the accompanying drawings which Figs. 6 and 7 are curves showing electromotive io'rce plotted in. the usual manner.

coil 2 namely, by having abscissas represent time and ordinates the electromotive force.

Fig. 8 is a diagram showing a modified form 01 apparatus and connections;

Fig. 9 is a diagram showing a further modification of apparatus and connections;

Fig. 10 is a diagram showing a further modification Fig. 11 is a diagram showing a particular mounting of unbalancing resistance;

Fig. 12 is a fragmentary view showing on an enlarged scale developed slip ring segments with unbalancing resistance con nected thereto.

Referring to Jhc drawings and first more particularly to Fig. ii an inductor generator ias its field coils *2 and 3 excited by means i. a direct current generator 1 acting an eXciter. The coils 2 and 3 are mounted is connected with the generator by conductors 62 and 63, a switch 66 serving to control the circuit of this coil. The coil 3 is conne ted with the exciter by means of conductors 6 end 67 its circuit being cou trolled by the switch 67. The coils 2 and 2-3 are oppositely wound so that they tend to force flux in opposite directions about the ring l so that the poles 5 and 6 are conscquent poles. Wound upon the poles 5 and 6 are coils 'Z' and 8 in which electromotive "force is induced the inductor 12 rot between the pole pieces 5 and These coi is are shown as so wound and connected in s'. ries that their elec romotive forces a e added so that the difference of potential at the terminals and 10 is equal to the sum of the clectr motive "forces generated in the coils 7 and 8. The inductor 12 is keyed to the rotating shaft 11 so that as the shaft is rotated the inductor will rotate between the poles 5 and 6 thereby varying the magnet-ism traversing the coils 7 and 8 and cans-- ing a corresponding induction of electrometive force in those coils.

Coil sections 23 and 24-. constituting a primary winding on the magnetic core 95.,

are connected across the terminals 9 and i of the generator by means ct cauldiutors 52 and 57; this circuit being controlled hr means o the switch silk .hc core 537 is shown as oil a horse-shoe shape having poles 536 and 27 and has its ciriit closed throi gh a magnetic block which is mounted on studs 28 and 29 0t non-magnetic material and is spaced from the member by means of non-magnetic washers 33 and 3%. Also mounted upon the core are coils 31 and connected in. seriesand forming a secondary winding. Connected with one terminal of the secondary winding through a switch tor coir-trolling the secondary circuit, is a noninductive resistance 39 from which the circuit leads through the variable resistance to the other terminal of the secondary winding. liiovisien is made for periodically short circuiting the resistance .;0 as follows: The conductor 61 leads trom one terminal 01? the resistance 10, through the switch blade LT, sliding contact stationary conti t 49 and conductor it to the brush 20, hearing successively upon c llector ring segmentsll, 16, 13 and 15, which turn with the generator shaft 11. The other terminal of the resistance 10 is connected by a switch 31 and the conductor with a brush 21 bearing upon the continuous collector ring 1!) which also turns with the shatt 11. The segments 15 and 16 are connected by conductors 17 and 18 of low resistance with the ring 19 so that when the brush 20 bears upon either the segment 15 or the segnumt- 16, the conductors 53 and 51 will he connected together and form a short ..-ircuiting shunt about the resistaine 4. so that this tance will he removed from the :ircuit o; the secondary above re rred to. There is provided a brush whicn is also adapted to bear on the segments 16, 13, 15 and 1t, which is connected by a conductor with the switch contact 18, so that when the switch arm ii? is thrown from the contact 19 to the contact t8, the brush instead of the brush 20, will be connected with one terminal oil" the resistance 10. lllnder these anntanccs, the short circniting ot the retance 10 will occur at difiln'ent angular POSltlOilS oi" the generator rotor, and consequently at dill'erent parts of the cycle of the generator electromotive force. As will be hereinat cr more particularly reterred to, the re. ance -10 may he so inserted as to cause either the p ""tive or negative magnetism in the. core to preponderate, and the shitting trom. one polarity to the other may be accomplished by moving the switch arm 1-7 from engagenuznt with the contact t8 to en i at with the mama if or vice YQJ'H}, thereby connecting either the brush 20 c as may be des le according to the pre imndcrating polainy of magnetism wanted. 7

Connected in parallel w ith the primary 3 3 and 2-1 across the geiaa'ator terminals 9 and 1.0. is a primary coil which has one terminal connected throiurh the switch it and the conductor 58 with the conductor 56 leading to the terminal 10, while the other terminal of the coil is -t'onnccted tlnwmgh the conductor with the conductor leading to the terminal 9. The primary coil 35 is mounted upon a magnetic core 36 having its circuit closed through a magnetic block 30, but a gap is formed in'the magnetic circuit by means of non-magnetic washers 33 and 3t mounted on the non-magnetic studs 28 and 29 upon which the yoke or block 30 is secured in position. Upon this magnetic core are wound the secondary coils 37 and 38 having their circuit closed through the switch 43, the non-inductive resistance 41 and the variable resistance The terminals of the resistance 12 are connected one through the conductor 59 with the coi'idnctor 53 and thence to the brush 21. while the other is connected with the brush through the conductor 55 so that this resistance is short circuited whenever the segment on which the brush 22 bears is connectml with the brush through one of the low resist ance connections 17 or 18 and the ring 19.

In explanation of the operations which take place, it a source of alternating electromotive force giving a curve of the general form as shown in Figs. (3 or 7, be connected to the terminals of a reactance coil, such as a transformer primary, the transformer will have, after a succession of cycles, an alternating magnetic flux in its core of equal positive and magnetic polarity, giving a curve of the general form shown in Fig. 4. The positive halt cycle or alternation of impressed electromotive force as indicated by the curve EFG of Figs. (l or 7 is opposed by a reactive electromot-ive force induced in the coil by the negative flux de creasing from maximum to ZQI'O to Fig. 41) and by'the positive flux increasing from Zero to maximum (l to l).

The negative halt cycle or alternation of impressed electromotive force, is opposed by a reactive electromotive force induced by the positive flux decreasing from maximum to zero (P to R) and the negative flux increasing from zero to maximum (R to S). Hence each alternation of the applied electromotive force is opposed by a reactive electromotive force induced by a flux variation equal to the sum of the maximum values of the positive and negative fluxes. However, during the first few cycles, the transformer flux may alternate with unequal magnetic polarity, the degree of inequality depending upon the instant of the electromotive force cycle that the switch is closed connecting the transformer primary to the source of electromotive force. If the switch be closed at the beginning 01" the positive alternation of the electromotive force (Figs.

' 6 or 7),then the entire first half cycle of the applied electromotive force is opposed by a reactive electromotive force induced by the increase of the positive flux only. Thereiore depending upon the nea iess oi the transformer core to saturation, the maximum flux P of the first cycle (Fig. may be nearly twice as great as the maximum positive flux P (Fi 4:) Where the magnetization curve is symmetrical. With each successive cycle, however, there is an inherent tendency decreasing the maximum positive flux and increasing the maximum negative flux until the flux alternates with equal positive and negative values.

lhere Will now be explained the cause of this tendency of the magnetization curve to assume a symmetrical form and the means for counteracting this tendency so as to cause the flux to alternate with any degree of inequality between the maximum positive and negative values or to be a flux of one magnetic polarity only, the former as shown as for instance in Fi 3, and the latter as shown in Fig. 2. This will be explained in connection with the apparatus of Fi 1.

In Fi 1 With an eXciting current supplied by the eXciter l to the exciting coils 2 and 3 so as to produce consequent poles at the poles 5 and 6, and With the switches 1-3, 4-4, and 51 open (that is with the secondary circuit of the transformer having the core 25 open and With connections to the primary on the core 36 open so that current is supplied by the generator to the primary on the core 25), if the generator inductor 12 be rotated from its horizontal position in a clockwise direction, the variation of the reluctance of the magnetic circuit, will cause variation of the flux through the indured coils 7 and 8. This will induce an alternating electromotive force in the coils 7 and 8, which Will ,be impressed upon the terminals 9 and 10, and alternating currents will flow through the circuit through the primary winding on the core 25 and, as previously referred to, after a succession of cycles of aternating current, the flux in the core 25 will be symmetrical as represented by the magnetization curve of Fig. 4.. The path otthe current through the primary circuit just referred to, is from the terminal 9 through the conductor 52, coils 23 and 2t, switch 46; conductor 57 and conductor 56 to the tern'iinal 10.

To simplify the explanation, let it be assumed that the number of turns in the coils 7 and 8 is equal to the number of turns in the coils 23 and 24; that all of the magnetic lines inclosing the electric conductors of the primary circuit, pass either through the generator coils 7 and 8 or through the transtiiormer core 25 that the electromotive i orce Wave is of the form shown by the curve in Fig. (3, that the flux through the coils 7 and 8 a minimum and the flux in the transioriner core 25 is zero When the inductor 12 is horizontal.

\Vith. the switches 4:3 M and 51 open,

as before referred i both to, so that the secondaries transformers and the primary oi one of the transformers is open so that only the primary consisting of the coils 23 and 2st is in circuit, if the rotor 12 be ro ated clockwise, starting from the horizontal, the flux through the coils 7 and 8 will increase until the inductor reaches vertical position. This increase of flux ll ind a positive e ectromotivc force in the generator coils T and S and :iorce a positive current through the orin 1 W1 x 1 2110.1 and will induce a posiinc trans;

4-1:. L J .0 once tn magnetising cuiient through the resistance referred to. Ther tore, 'hen the inductor 2 reaches its vertical position, the generator flu will be a maximum and also the transformer flux will be a maximum the generator flux equaling the transformer flux plus an amount which the generator flux exceeds the transformer flux, which amount is occasioned the excess variation ov nerator flux, as before referred which is nec current throus i the o ary to rorce the magnetizing nine resistance Oi the l flux born represented b 1n As tee generator inuucbr 12 rotates rrozn the VOIiiCftl. the aerator in decreases. This cause. a neon. We electromotive force to 1 he induces. in the generator coils a and S. The transit riner flux also decreases. As the transformer flux decr :scs, it induces e tive reactive electroinotire forc in the the former )rimarv coils 2 2i zinc during the inter ii the t: ill-3!. flux is decreasing fronl i'he ll o" 'A Q O i n lumc'! i H in llulilwhl .1 1. 3 silo (1' use ldv Qt L lle transformer inagiunsni exceeds the decrease of the generator magnetism by an amount :uch that the l'Oi-lCilfQ electrometive "force of 'L'liO pq-nnar coils exceeds th; of the gen- .e the magnctizaing rurre t through the ohmic reels"- ance of the iiar'v circui rherclere. when the t siioriner magnetism has dc: rrcase to its residual value. the generator (7 will exce d the trait, .i'nier liur if. :1. cc ain amount which is occasioinwl liv i s' .Q'reatcr rate oi increase (lu i its loss rate or deert During the interval that flu is decreasing from the maxiuunr a nil,

"- force adequate to force the magnetizing cur- Lair rent through the ohmic resistance of the primary circuit. Therefore, when the transformer flux has decreased to zero, the relation of the generator flux to the transformer flux is that the generator flux is equal to the transformer flux plus the amount which the generator flux exceeds the transformer flux at point Q of the curve in Fig. 2, as above referred to, minus the flux due to the excessive decrease of the generator flux over the decrease of the trans .)l'l1l0l. If, therefore, X represents the generator flux, Y. the transformer l'iux, Z the amount by which the generator flux exceeds the trans former flux at point P, W the amount of flux by which the generator flux exceeds the transformer flux by reason of the greater decrease of the transformer flux from the point P to the point Q in Fig. 2 and V the amount of flux difference be ween the generator flux and the transformer flux due to the difference of decrease of these fluxes between the points Q. and R of the magnetization curve in Fig. 2, then the relation of the fluxes is shown by the equation X:Y+Z+VV, but at the point B, Y is equal to consequently at this point the generator flux is shown by the equation, X:ZllV -V. Z-l-lV-fih however is the amount of flux due to flux variations to produce electromotive forces for overcoming the ohmic losses of the primary circuit and may be represented as a whole by the character t. It thus'appears that there is still some generator llnx at the time that the transformer flux is zero. Vhile this ro maining [lux in the generator is decreasing to zero, as the inductor 12 moves into its horizontal position, the flux variation starts "*fithe reversal of the magnetic polarity of the transformer flux and produces the line R-S below the horizontal axis H. As the generator inductor again turns from the horizontal. the generator flux increases as before and the transformer flux riss along the dotted line to a point p which is below the point ,0 in Fig. 2. As the generator tlnx again. decrea to zero (the inductor turning from the vertical to the horizontal), the transformer flux decreases to zero and with a reverse polarity to a point S 3 below the horizontal e s, the maximum value ,3) being less than the maximum P. So with each successive cycle the maximun value of the. positive transformer fiux decreases and the value of the negative maximum transformer tli increases until the transformer magc nates with the poitive and negati\ maximums equal in amount as shown in Fig. t, when the values of Z, \V and V above referred to, which are the amounts of flux corresponding to variations required to pro duce electromotive forces to overcome the ohmic losses in the primary circuit during the positive portion of the magnetization curve, are respectively equal in amount to the corresponding flux quantities during the negative portion of the magnetization. Therefore, when the maximum negative transformer magnetism is equal in amount to the maximum positive trans'tbrmer magnetism, there no further change in the relation of these maximums, and the algobraic sum of the flux variations required to overcome ohmic losses as referred to above, is zero. Since the generator flux which exists when the transformer flux has decreased to zero, (this being the inherent force causing the change in the relation of the maximum positive and negative transformer fluxes) is equal in amount to the excess of the flux variations required. to overcome ohmic losses of the positive current over the flux variations required to overcome ohmic losses of the negative current, then if the algebraic sum of the flux variations required to overcon'ie these ohmic losses were reduced to zero, the generator flux existing at the time of zero transformer flux, would also be zero. The relation of the generator flux to the transformer flux would then be the same at the end as at the beginning of the cycle. each successive cycle would begin. and end with the same relation of generator flux to transformer flux and of positive and negative transformer fluxes. Consequently the transformer flux would be a varying flux of one magnetic polarity only, following the general curve of the solid line inFig. 2. So long, however, as the algebraic sum of the flux varia 'ous required to overcome the ohmic loss does not equal zero. the transformer flux will have a value at the end of the cycle, ditli'erent from the value at the beginning of the cycle. Consequently the relation of the positive and negative maximum transformer fluxes will change with each successive cycle until. there exists such relation of this maximum that the algebraic sum of the flux variation required to overcome the ohmic losses is zero. Conversely, if the relation of the maximum positive and negative transformer fluxes remains unchanged during a succession of cycles, then must. the algebraic sum of the fluxes requirecl to overcome ohmic losses, be zero.

In the foregoing discussion, it has been assumed that a circuit has been completed only tlni ugl the primary consisting of the coils 2 and across the terminals 9 and 10 of the generator. lf. now. the switches and 51 are closed, the secondary circuit of the trans owner will be closed through the secondary coils 31 and. 82, and the resistances 39 and 40. It has already been seen that the portion of the resistance 40, included inthe secondary circuit, is adapted to be short circuited at certain portions of the revolutions of the inductor 12 of the generator, this short circuit taking place through the brushes and 21 and the ring segments upon which they bear. These segments are so arranged and connected and the brushes mentioned so placed upon them, that the shunt about the resistance 40 will be open, and consequently the resistance 4L0 inserted in the secondary circuit, while the inductor is rotating from the horizontal to vertical. During the interval that the inductor is rotating from the vertical, the shunt path through the brushes about the resistance 40 is closed so that this resistance is cut out of the secondary circuit. it it be assumed that the secondary current which flows when the inductor is rotating from the horizontal to the vertical is positive, and that the secondary current which flows when the inductor is rotating from the vertical to the horizontal, is negative, it will be apparent that the negative secondary current will exceed the positive secondary current by an amount depending upon the value of the resistance ltl. The excess of negative secondary current will be supplied by an excess of negative primary current which will cause an excess of negative ohmic losses in the primary circuit and consequently the algebraic sum 01 the flux variation required to overcome ohmic losses will no longer be zero. Hence there will be an inherent force as before referred to, causing the relation of the positive and negative maximum transformer fluxes to continue to change until said algebraic sum is equal to zero. The amount of said change will depend upon the amount of the excess negative current are '"erred to, which in turn depends upon the value of the resistance 40. It the resistance it) be adjusted to such a value that the excess of negative curr nt will cause an additional flux variation of minus t, where equals Z+lVV, to overcome ohmic losses in the primary circuit, then the relation of the positive and negative maximum transformer fluxes will continue to change until the transformer flux is a varying flux of one magnetic polarity only, giving a curve of the general form of the solid line of Fig. 2. It the resistance be adjusted to an amount less than that required to produce the flux variation t, the transformer flux will be an alternating flux with the maximum polarity of ditlerent signs unequal, giving a curve of the general form of Fig. 3. If d0 be adjusted to an amount greater than that producing the flux variation. 6, then the transformer flux will be a varying flux of one polar ty only, but not decreasing to zero, and giving a curve of the final form as in Fig. 5. WVhere the alternating transformer flux is of equal positive and negative maximum values as in Fig. l, the positive magnetizingcurrent equals the negative magnetizing current, while with the transformer flux of unequal positive and negative maximums, as in Fig. 3, or a flux of one polarity only, as in Figs. 2 or 5, the positive magnetizing current exceeds the negative magnetizing current in the primary circuit, but in each instance, the negative load current in the primary circuit required to supply the negative load current in the secondary is sufliciently in excess of the positive load current in the primary circuit required to supply the positive current in the secondary circuit, that the combined load and magnetizing negative currents in the primary circuit is equal to the combined load and magnetizing positive currents in the primary circuit. Therefore a periodic unbalancing of the secondary current will not cause an unbalancing of the total current in the primary circuit, except during the interval ot the succession of cycles when the relation of the positive and negative maximums oi transformer magnet-ism is changing to cause such unbalancing of the magnetizing current as will neutralize the unbalancing ot the load current.

A further explanation is that the increase of the transformer flux is opposed by the secondary current, also the decrease of the transformer flux is opposed by the second ary current. The amount of opposition depends upon the amount or secondary current, hence by increasing the secondary current during the interval of the negative (demagnetizing) current in the primary circuit the secondary opposition to the demagnetiziug of the traustormer core exceeds the secondary opposition to the magnetizing of said core. 7

It the switch arm 47 be moved from ongageinent with the contact l9 into engagement with the con ct 48, the short circuiting shunt for the res1stance it) will be formed throughthe brushes 21 and instead of through the brushes 230 and 21 as previously noted. The, brush is placed substantially removed from the brush 20 so that the shunt will be closed and the resistance 40 removed from the secondary circuit when the inductor 12 s moving from the horizontal to the vertical and hence there will be an excess of positive secondary current during this interval. This operates to reverse the polarity 01 the transformer flux, which is necessary in order to cause an excess negative magnetizing current to neutralize the excess positive load current, thereby-balancing the total current in the primary circuit. It should be noted that this reversal is made without in any way alte ing the connection of the generator to the primary magnetizing coil of the transformer and with only an instantaneous unbalancing of the total current in the primary circuit.

lVith all switches closed as shown in Fig. 1, the transformer cores and 36 will be magnetized so that the flux in the core 25 will be a maximum when the flux in the core 36 is a minimum. The connection of the generator terminals to the primary coils 23 and 24, is the same as the connection to the primary coil 85. The core fluxes are, however, in quadrature and differ in magnetic polarity, because the secondary coils Sland 32 have the resistance 10 in their secondary circuit, short circuited during the interval of negative current, while the secondary coils 37 and 38 have the resistance 42 in their secondary circuit short circuitcd during the interval of positive current.

In the diagram of Fig. 8, the generator is arranged as shown in Fig. 1, and the transformer primaries 23 and 24 are adapted to be connected across the generator terminals 9 and 10. The elements of the generator and the transformer are the same as the construction illustrated in Fig. 1 and the same refcrence numerals have been applied thereto.

There is, however, a switch 74 inserted in the primary circuit. The secondary circuit of the transformer including the secondary coils 31 and 32, is, however, modified so that in addition to including the resistances 39 and 40, it also includes a transformer having the primary windings 72 and 73 connected in series with the resistances 39 and 4.0 in the circuit of the secondary coils 31 and 32. A switch 7 6 is inserted in this circuit. The primary windings 72 and 73 are wound on a magnetic core consisting of the ring 71 providing a closed magnetic circuit, and also the open ring 68 having the poles or ends 69 and 70. \Vound upon this core is a short circuited secondary coil 145. The apparatus of Fig. 8 is also provided with switching mechanism comprising the stationary contacts 48 and 4:9, and the movable contact 50 secured to the pivoted switch arm 17 Except as above stated, the connections are the same as those described in Fig. 1 and the same reference numerals have been used for like parts in the two figures.

With the switches set as shown in Fig. 8, if the inductor rotor 12 be rotated in a clock wise direction, let it be assumed that the path of the primary current through the coils 23 and 24 will be from the terminal 9 through the conductor 77, switch 74, coils 23 and 24, and conductors 78 and 79, to the other terminal 10 of the enerator. During the positive half cycle, tie path of the sec ondary current will be from one terminal of the winding 31 through the resistance 39, conductor 84, switch 7 6, winding 73, winding 72, conductor 83, conductor 85, resistance 10, to a terminal. of the secondary winding 32. During the interval of the negative half cycle, the secondary current. has a shunt around the resistance 10 as follows: from the conductor 85 through the switch arm 17, con tact 19, conductor 81, brush 20, collector segment 15, connector 17, ring 19, brush 21, conductor 80 and switch 75, to the adjustable arm contacting with the resistance 40. If the resistance 40 be adjusted as explained in connection with the apparatus of Fig. 1, the transformer flux in the core 25 may be a varying flux of one magnetic polarity only. The secondary current, however, of this transformer, acts as an unbalanced primary current in the windings 72 and 73 of the transformer having the core 68. The flux in the core 71 and 68, will also be a varying flux of one polarity only. This will appear from the explanation made in connection with the apparatus of Fig. 1, as it was there set forth that the unbalancing of the transformer flux was caused by the reaction on the primarv circuit and the unbalancing of the ohmic losses therein.

As explained hereinhefore, the flux in the core 25 is a maximum when the inductor 12 is vertical. The flux, however, is a maximum in the core 68 and 71 when the inductor is horizontal. It should be noted that the only magnetizing current supplied by the generator, is a balanced alternating current supplied to the primary winding and By a periodic variation of the lQSlSttlDCG in the secondary circuit, however, where the. resistances are different for dillerent polarities, the alternating energy supplied to the primary winding. so distributed between the windingsi l and 24 and the windings 72 and 73fas to induce a varying flux of one polarity in the core 25 and a varying flux of one polarity in the core comprisingthe rings 68 and T1, the flux in being in quadrature with the flux in G8 and 71.

The polarity of the flux of the core 25 and also that of the flux of the core 8 and 71 is reversed by moving the 1(*.\'(.l. illg switch arm 17 so that the contact 50 engages with the contact 18 instead of the contact 49. It should be noted that this reversal of polarity is made without any change of the connection of the generator terminals to the magnetizing windings.

Referring to Fig. 9. the generator field structure comprising the ring 91 and the pole pieces 89 and 90, are arranged as in the generator of Fig. l. The exciting coils.

-87 and 88 are connected in parallel across the exciter generator 86, by a switch 10% the poles S9 and 90 being of opposite pr la-rity as is well understood. )2 represents a single phase alternating current winding .he secondary circuit.

ild segments just referred to are rotated by neans oil a synchronous motor 119 which is r n the conductors 12%) and 130 3 in L connected to the other terminal of the, secondary of the transformer. The molor 119 will. therefore rotate in synchonism ='iih the g aerator 11o that the eilect noon the tr rmer secondary circuit \vlll be the san'io as ii the colicctor rings were mounted upon the shaft of the generator as i ginbefore referred to, and the llux in the core oi? the transformer having the primary 1:. t be unbalanced between the two polarities or have a single polarity only by zuljusting the resistance 40 as has been he- :tore explained.

Referring now to Fig. 11, the generator comprises poles and (*7, induced windings T and S and inductor 12 mounted on the shaft ll Qcollector segments and ring 13 to 16 inclusive and brushes and 2" bearing thereon as described in connection with Fig. 1.

al-so the apparatus of F ig. 11 has a transformer conmrising a core 25 having primary coils 23 and 2st thereon connected across the tern'iinals 9 and of the generator and having;- secondary .vindings 31 and 22 connected to the brushes 21 and 22 by means of the conductors H1 and 14:2 and the switch 14rd: in conductor H1, all as described in connection with the apparatus of l ig. l. The primary transitornler "ircuit is controlled by a switch 112? while the secondary 'cr t is controlled by switch 14$, but instead of having a resisfimce l0 external to the generator structure as in Fig. 1, in the present case the resistances 13S and liii are connected on the one hand between the segments H- and 15 and on the other hand between the segments 13 and 16. It will be apparent from observation of Fig. 11 that when the brush 22 is in contact with either the segment 15 or 16, the secondary circuit of the transformer will be closed through either the connection 17 or the connection 18. \Vhon, however, the brush 22 is upon either of the segments 13 or 14, the resistance 139 or 138 will be inserted in the secondary circuit. The effect of this periodic insertion of resistance has been before explained. collector ring segments 1?, to

inc inclusive, may be tormed after the mannor of a conunutator, that by comlucting bars separated by insulating pieces. As illustrated in the fragmentary view of Fig. 12, the segments l t and 15 are shown as separated b a block of insulation with the resistance 138 spanning the insulation and connecting the segments ll and 15 together.

For the purpose of simplifying it has been assumed in connection with foregoing explanations that the sum of the turns of the generator windings 7 and S is equal to the sum of the turns of the transformer primary windings 2? and It will be understoml, however, that the operation of the invention is not dependent upon any exact relation between these turns. It was also assumed for purposes of explanation that the electromotivc force curve was of the form shown in Fig. (l, but the operation oi? this invention does not depend upon any articular form of, cur vc. Also thecxplanaliUllS assume that all of magnetic lines inclosing conductors of the primary circuit pass either through the generator coils 7 and 8 or through the transformer core .35, but it has been explained that if the transformer flux continues through a succession of cycles with any degree of inequality between maximum positive and maximum negative, the addition of line inductance to the primary circuit will not destroy this relationship (as the algebraic sum of flux variations due to line inductance when taken after an entire cycle, is zero) providing the brushes have sullicient lead so that the increase ot the primary circuit is during the interval of the proper halt cycle of the primary current. It is important for economical operation, that during the entire in terval of negative (or demagnetizing) primary current, there shall be a synchronous decrease of the secondary circuit, thereby allowing a sufficient secondary current to prevent the reversal of polarity of the primary current. This is espi-rcially important when the magnetic circuit is open (see non-magnetic washers 33 and 34:) as a very little primary demagnetizing energy will reverse the flux in 25, unless said domagnetizing energy is opposed by a secondary current which absorbs the greater part of said demagnetizing energy. The best results have been obtained by so proportioning the slip ring segments, that the interval of synchronous decrease of the secondary circuit is greater than one-half cycle. This avoids the necessity of determining the exact neutral position of the brushes.

In the arrangement of Fig. 8, the inclusion of the reactance of the primary coils 72 and 73 in the secondary circuit of the trans "former having the core 25, interferes to some extent with the secondary current which opposes the dei'nagnetizin g of the core 25 so that a larger adjustment of the resistance 4:0 is required than would be the case if the coils 72 and 73 were not in the secondary circuit.

What I claim is 1 1. A means for exciting by an alternating current, magnetic flux of which flux of one polarity predominates over the flux of the other polarity, comprising in combination an exciting winding for producing flux, means for applying alternating current to said winding, a secondary winding in inductive relation to said primary winding and means for increasing the ohmic resistance of the circuit of said secondary winding during one alternation of current over the ohmic resistance of said secondary circuit during the next preceding current alternation.

2. The method of producing an asymmetric alternating flux from a source of symmetrical alternating E. M. F. in an apparatus comprising a magnetic core, a primary winding thereon supplied from said source, a second winding thereon in inductive relation to said primary winding, and an impedance in the circuit of said secondary winding, which comprises cyclicly varying the value of said impedance synchronously with the E. M. F. of said source.

3. The method of producing an asymmetric alternating flux from a source of symmetrical alternating E. M. F. in an apparatus comprising a magnetic core, a primary winding thereon supplied from said source, a second winding thereon in inductive relation to said primary winding, and an impedance in the circuit of said second winding, which comprises controlling the magnetomotive force of said second winding so as to produce unequal reactive effect during successive half cycles of the source of E. M. F.

4. The method of producing a unidirectional pulsating flux from a source of symmetrical alternating E. M. F. in an apparatus comprising a magnetic core, a primary winding thereon supplied from said source, a second winding thereon in inductive relation to said primary winding, and an impedance in the circuit of said second winding, which comprises controlling the magnetomotive force of said second winding so as to produce unequal reactive efiect during successive half cycles of the source of E. M. F.

5. The method of producing a unidirectional pulsating flux and the method of reversing the magnetic polarity of said flux from a source of alternating E. M. F. in an apparatus comprising a magnetic core, a primary winding thereon supplied from said source, a second winding thereon in inductive relation to said primary winding, and an impedance in the circuit of said sec ond winding which comprises controlling the magnetomotive force of said second winding so as to cause the reactive eflect during the half cycles of one sign of a succession of cycles of E. M. F. to be in excess of the reactive elfect of the half cycles of the opposite sign of E. M. F. and the changing of said excess reactive efiect to the half cycles of the opposite sign.

' JOSEPH N. GILBERT.

Witnesses:

J OHN A. HAAS, NOTRA PAPAZIAN. 

